ABSTRACT Alcohol misuse is most prevalent among individuals in their late teens and early to mid-twenties, and the peer- intensive environment is a primary influencer of alcohol use and its associated consequences. Most alcohol prevention and intervention programs for young adults do not include peers as a part of the intervention, and so do not result in culture change. Bystander intervention training, which is grounded in theories of prosocial helping, focuses on educating people about risky situations and encouraging them to take action to help others reduce their risk. The applicability of bystander intervention for prevention of problematic alcohol use is obvious, but the development of this promising new direction for alcohol intervention is hindered by the current lack of valid and reliable measures of the multiple pertinent constructs. Established researchers with expertise in college alcohol use, bystander intervention, and qualitative and quantitative methods will use guidance from theory, current measures from sexual assault bystander intervention, and a rigorous mixed methods approach to develop a battery of valid and reliable instruments for use in alcohol-related bystander intervention research and programming. The specific aims are to: (1) identify alcohol bystander-related constructs and related survey items utilizing focus groups with young adults (8 groups; N = 64 participants), (2) refine the measurement constructs and items using cognitive interviews with a separate sample (N = 20), and (3) conduct a thorough psychometric evaluation of the derived instruments using a nationally representative panel of young adults (N = 600). Eight established bystander constructs that will serve as a starting point are: readiness to help, perception of peer helping and peer approval of helping, intent to help, bystander self- efficacy, barriers to helping, consequences of intervening, and bystander behaviors. Analysis of focus group data will include open and axial coding of transcripts by multiple coders; the cognitive interview methods will include structured probes about item content and directed modification of survey wording; the psychometric evaluation will use factor analysis, item response theory, test-retest reliability, and convergent and discriminant validity evaluation for all of the measurement instruments. This proposal has the potential to have a strong impact because federal guidelines now recommend implementing BI training programs on college campuses for all incoming students. This research will produce a set of psychometrically sound measures that will be aligned with the putative mechanisms of bystander intervention programs, thus ensuring the accurate program evaluation and cross-study comparison necessary to build better interventions to address alcohol misuse and its associated problems among young adults.